The broad aims of this project continue essentially the same as before - namely to investigate the various factors that govern the nature of the folding, or conformation, of a protein chain which determines its biological activity. In particular, the following studies will be taken up and completed as far as possible, during the next year. 1) The accuracy of the potential functions used for conformational analysis will be tested by comparison with X-ray, IR and NMR data. Already there are indications that the commonly used torsional potential functions require appreciable changes, and these will be pursued. 2) The study of the backbone conformation of cyclic tetra, penta and hexapeptides will be extended to that of the side-chains also, with both normal and N-methylated peptide units. Potential functions for the O--H...O hydrogen bond will be worked out. 3) Antibiotic structures containing L- and D-amino acid residues will be studied. In particular, the restricted conformational flexibility of alpha-methyl alanine in antibiotics like alamethicin will be explored. The structural role of Beta-alanine in the chemical activity of peptides in relation to the large conformational flexibility for this amino acid will be explored. Also, the detailed structure of the cyclic pentapeptide malformin will be investigated. 4) This method of analysing crystal structures from packing studies will be explored further in compounds having higher symmetry.